Stardome educator, Josh Kirkley, dives into the exciting topic of our search for life outside of Earth.

Why water?

Earth has always been the stand out planet in our Solar System. Not only are we the only known planet with life, but we are also the only known planet to hold bodies of liquid water on the surface.…and that’s important. All living things require water. We do not know any type of life that can go without it, so it makes sense that we look for water when searching for life outside of Earth.

So far, all the other planets have shown no signs of life at all, or even large bodies of liquid water like Earth. Venus is too hot, and Mercury’s proximity to the Sun sterilises the planet with high doses of radiation. The gas giants have no solid surface, let alone any water, so it’s highly unlikely they harbour any type of life. Billions of years ago, Mars did have oceans and possibly even life, but not anymore. Today it’s a cold desert that lost its oceans when they evaporated into space. We only see tiny quantities of flowing water down the side of craters during the summer months, but it’s still very little. It holds some water at its poles and in frozen quantities underground, but it’s unlikely that any significant kind of life could thrive in this hostile environment today.

These factors make Earth look like the only planet in our Solar System that has life. But planets are not the only places we look for life anymore. Within the last few decades, scientists have been turning their eyes to some even more fascinating worlds than the planets; their moons.

Europa – Water world of our Solar System.

Europa, an icy moon of Jupiter, was first observed by Galileo Galilei in 1610. We knew nothing about this moon until the Pioneer missions in the 70’s provided us with our first grainy images of the surface. The Voyager missions followed in the 80’s, sending us our first clear images of Europa’s surface and leading scientists to speculate that an ocean could be hidden beneath the icy shell.

In the 90’s, NASA followed up on this speculation, sending the Galileo mission to Jupiter. The spacecraft made several close fly-bys of Europa and gave us much of the information we know about the moon today. It heralded some amazing results by scanning the surface in incredible detail and revealing a moon that is covered in a criss-cross of lines and cracks. Much to our surprise, we also discovered that Europa is almost completely crater-free with the smoothest surface of anybody in our SolarSystem.

The discovery revealed that Europa has a young surface, indicating that something geological was occurring beneath the surface. NASA observed Europa in 2012 with the Hubble telescope and it captured what appeared to be jets of water spraying out into space from the poles. Further observations in 2016 confirmed this discovery, and we now know that Europa does indeed hold a huge ocean of water beneath its surface. So much so, it is believed that Europa holds twice as much liquid water as Earth!

Alien life – What could be down there?

So, if Europa does have an ocean, does it have life? A question scientists have been asking for years. This far-out world may very well be the first place we discover alien life. It is hard to think of what life on Europa may look like but we can get some ideas by looking at Earth life. In the depths of Earth’s ocean trenches, we find some of the strangest beings on our planet. Fish that glow, squid with huge eyes, and aquatic beings that seem to be the stuff of science fiction. As scary as deep ocean life on Earth appears, they are a good indication of what life on Europa may look like.

Light does not penetrate very far down into our oceans and the majority of Earth’s seafloor is pitch black. Creatures have learnt to live in this hostile environment, adapting to their surroundings over millennia through evolution. Some have learnt the trick of bioluminescence, creating their own artificial light to draw in potential prey for a meal without the help of sunlight. Europa’s oceans are likely to be very dark too. It’s unlikely that sunlight is able to pass through the icy crust.

If life does exist on Europa, it is plausible that they may resemble deep sea creatures here on Earth. Maybe we will find squid-like creatures that have also learnt how to harness bioluminescence in their favour. We won’t really know until we go there. Both NASA and ESA are developing plans to explore Europa in the 2020s and into the 2030s. Some of these missions may even carry a lander that could drill down into the surface and dive into the ocean beneath. It’s a tantalising thought wondering what these future missions may hold, but until then, we wait.

Image: Close up of Europa’s surface cracks. Credit: NASA.

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